The mouse ldh-3 gene codes for the lactate dehydrogenase-C isozyme and is expressed only in male germinal cells at a specific stage of sperm development. Our research objectives are to: 1. Clone this gene from the DNA of mouse germinal (spermatocyte and post-meiotic spermatid) and somatic cells, using as a probe cloned cDNA made from LDH-C mRNA purified from mouse spermatocytes; 2. Characterize and compare the microstructure of the cloned genes, by restriction, electron microscope and DNA sequence analysis; 3. Examine mRNA biosynthesis by (a) isolating the primary transcript and processing intermediates at successive stages of spermatocyte development, using cloned DNA as a probe, and (b) determining the developmental timing and order of processing steps by in situ hybridization of DNA probes to size-fractionated RNA; 4. Study transcriptional control by microinjection or gene transfer of cloned DNA into normally non-producing cells, by introduction of cell sub-fractions into both producing and non-producing cells, and ultimately by in vitro studies in a partially purified system; 5. Clone, for comparative analysis of structure and expression, the genes coding for the LDH-A and LDH-B isozymes, which are expressed in somatic cells under different developmental and tissue-specific controls, using LDH-C DNA as a probe; 6. Determine chromosomal map location of the three genes by in situ hybridization of cloned DNA to mouse chromosomes and by restriction analysis of DNA isolated from mouse-hamster somatic cell hybrids.